Rotary-type selector switches have long been used to control the operation of electrically-powered material handling vehicles, such as fork lift trucks and the like. Normally these types of switch assemblies have a plurality of switches therein which are selectively actuated to change the resistance between a power source, such as a battery, and an electrically-operated drive member.
One type of rotary selector switch assembly which has been previously used for control of vehicles of the type referred to above is disclosed in U.S. Pat. No. 3,493,696, which is assigned to the assignee of the present invention. This particular switch assembly consists of a plurality of modular components which each have a switch supported therein and are interconnected to form a plurality of switch units that can be operated utilizing a single rotatable member having cams thereon. While this type of unit has found a remarkable degree of commercial success, manufacturers are constantly striving to improve the efficiency of such a switching system or assembly, reduce its complexity and also, at the same time, reduce the manufacturing cost and assembly time.
One type of control circuit that has been utilized for varying the speed of a vehicle such as a fork lift is what may be commonly referred to as a discrete or step-controlled circuit. This type of circuit incorporates a power source connected in series with a plurality of resistors to a field-winding and an armature of an electrical motor. Parallel switches extend across the resistors and parallel circuits are provided so that reverse current flow can be developed through the armature and, at the same time, selected numbers of resistors can be by-passed to vary the speed of the vehicle.
More recently, a stepless or solid-state control has been developed which includes a variable potential control device as well as a plurality of switches interposed between the field-winding and armature of a battery or power source.
One of the problems encountered in switching systems of this type is to have the capability of providing accurate adjustment of the components for any given vehicle motor.